Great essay, and awesome graphics. Crinoids are about the only creature stranger than echinoids and must have been the inspiration for some H.P. Lovecraft stories. I owe you one on sea cucumbers.
Bradley, thanks for the compliment! You are absolutely right on the strangeness of crinoids! Their common name, sea feathers says a lot. When we lived in northern Alabama, the stems of crinoids were one of the most common fossils in the Devonian (I think) limestone. So crinoids have been around for a long time, as weird today as they were then.
Years ago, my husband’s parents used to sell these postcards in their rock shop for 10 cents apiece. I’ve read that the little “doves” that are found inside the shell are the creature’s teeth.
Sand dollars certainly have a native charm. The "doves" are indeed the parts of the mouth apparatus called "Aristotle's Lantern". It has radial, 5-part symmetry. In sand dollars, the tips cannot be protruded from the mouth (as they can in sea urchins) so it is not clear how they function in concert with the food grooves. Maybe the teeth scrape algae off sand grains? Just guessing.
Great essay, and awesome graphics. Crinoids are about the only creature stranger than echinoids and must have been the inspiration for some H.P. Lovecraft stories. I owe you one on sea cucumbers.
Bradley, thanks for the compliment! You are absolutely right on the strangeness of crinoids! Their common name, sea feathers says a lot. When we lived in northern Alabama, the stems of crinoids were one of the most common fossils in the Devonian (I think) limestone. So crinoids have been around for a long time, as weird today as they were then.
Here’s another perspective on the sand dollar:
https://www.ebay.com/itm/297244154667
Years ago, my husband’s parents used to sell these postcards in their rock shop for 10 cents apiece. I’ve read that the little “doves” that are found inside the shell are the creature’s teeth.
Sand dollars certainly have a native charm. The "doves" are indeed the parts of the mouth apparatus called "Aristotle's Lantern". It has radial, 5-part symmetry. In sand dollars, the tips cannot be protruded from the mouth (as they can in sea urchins) so it is not clear how they function in concert with the food grooves. Maybe the teeth scrape algae off sand grains? Just guessing.